Oscar Pistorius' emotional -- sometimes even theatrical -- reactions to grisly witness testimony show a man who appears to be deeply disturbed about the night he claims to have accidentally shot and killed his girlfriend.

As his premeditated murder trial has gotten underway this week in Pretoria, South Africa this week, the Paralympic Blade Runner has sobbed, covered his ears and hung his head as witness after witness has testified about the night Reeva Steenkamp died.

PHOTO: Oscar Pistorius, listens to evidence from a witness speaking about the morning of the shooting of his girlfriend Reeva Steenkamp, in court on the fourth day of his trial at the high court in Pretoria, South Africa, March 6, 2014.

Werner Beukes/AP Photo

PHOTO: Oscar Pistorius puts his hand to his face in court on the fourth day of his trial at the high court in Pretoria, South Africa, March 6, 2014.

Judge Thokozile Masipa, who will decide the athlete's guilt or innocence, will likely be looking at Pistorius' reactions, Jules Epstein, a law professor at Delaware's Widener University and former criminal defense attorney, told ABCNews.com.

"If there is any sense at all that he is faking it, an experienced judge who picks that up will have trouble ignoring it," Epstein said.

Alon Skuy/AP Photo

PHOTO: Oscar Pistorius in court on the third day of his trial at the high court in Pretoria, South Africa, March 5, 2014.

The athlete shook slightly and sobbed today as Johan Stipp, a radiologist, testified that he went to Pistorius' house after hearing shots and screams on Valentine's night last year. He was one of the first people to arrive.

Stipp said he noticed a wound in Steenkamp's right thigh, in her upper arm and to the right side of the head, with brain tissue around the skull.

"She had no pulse in the neck, she had no peripheral pulse. She had no breathing movements that she made," Stipp said.

He also added that Pistorius looked "sincere" after the shooting and said he had mistakenly shot Steenkamp because he believed she was a burglar.

Epstein said Stipp's testimony and Pistorius' reaction could help support the athlete's story.

"In terms of the immediate minutes after the event, it should be pretty powerful evidence that this was an accident," he said.

It was an especially emotional day for Pistorius, who held rosary beads in court today to mark the anniversary of his mother's death.

Alon Skuy/AP Photo

PHOTO: Oscar Pistorius puts his hand to his face at the end of the day in court on the third day of his trial at the high court in Pretoria, South Africa, March 5, 2014.

Mike Hutchings/AP Photo

PHOTO: Oscar Pistorius holds his head in court on the third day of his trial at the high court in Pretoria, South Africa, March 5, 2014.

Earlier this week, Pistorius had covered his ears as his attorney challenged a witness, at one point arguing that Steenkamp could not have screamed after Pistorius fired a first shot through a bathroom door because that bullet had likely struck her in the head and caused serious brain damage.

Pistorius' lawyer Barry Roux made the claim as he tried to poke holes into the testimony of a witness who said she heard a woman scream after a first shot. That scream was followed by several more shots in quick succession, Pistorius neighbor Michelle Burger had told the court.

Marco Longari/AFP/Getty Images

PHOTO: Oscar Pistorius looks at his notes during the fourth day of his trial for the murder of his girlfriend Reeva Steenkamp at the North Gauteng High Court in Pretoria, March 6, 2014.

Werner Beukes/AP Photo

PHOTO: Oscar Pistorius listens to evidence from a witness speaking about the morning of the shooting of his girlfriend Reeva Steenkamp on the fourth day of his trial at the high court in Pretoria, South Africa, March 6, 2014.